This invention relates to a socket for removably mounting an electronic part which has a large number of terminals on its lower surface and for electrically connecting each terminal to external equipment and more particularly to a socket which is suitable for BGA (Ball Grid Array) packages.
Generally, resin sealed IC packages are subjected to an electrical property and/or reliability test called a burn-in test prior to their shipment from the semi-conductor manufacturer in order to distinguish between acceptable and defective products. In electrical property tests, the input-output characteristics, pulse properties, noise leeway, and the like, of the IC chip are tested. According to the burn-in test, on the other hand, IC packages which have passed the electrical property test are arranged in an oven and are operated for a certain period of time at a power source voltage which is approximately 20% higher than the rated value and at an elevated temperature, such as 125xc2x0 centigrade, for example. IC packages found to be unsatisfactory in the burn-in test are separated with only those IC packages that continued operating satisfactorily shipped out as acceptable products.
BGA packages having terminals comprising spherically-shaped solder balls arranged in a selected matrix such as in a zigzag fashion on the lower side of the package have become popular. Among the advantages of BGA packages are: the terminal pitch can be widened while maintaining a small outside dimension and the terminal is sturdy, thereby making it less likely to be damaged in case of engagement with some other part.
FIGS. 10(a) through 10(c) show prior art sockets for burn-in tests for loading a BGA package. As shown, socket 101 has a square base 102 made of resin and, on base 102, a slider 103 for mounting the BGA package 100 is arranged for movement in the horizontal direction for the purpose of mounting BGA package 100. A cover 104 made of resin and having an opening 104a is disposed on top of base 102. Cover 104 is movable upwardly away from the base and downwardly toward the base by a compression coil spring 105. A bore is formed through slider 103 and base 102 that corresponds to each solder ball 100a of the BGA package. A contact 106 for the pressure connection of solder ball 100a of the BGA package is so arranged as to run through respective bores of slider 103 and base 102. Each contact 106 is made of a longitudinal metallic member having a tip end formed with a pair of arms 106a and 106b . As shown in FIGS. 10(a) through 10(c), each contact 106 is fixed to base 102 and extends in a direction generally perpendicular to the top and bottom surfaces with arms 106a and 106b facing upwardly. As shown in FIG. 10(c), contact 106 is formed in such a way that arms 106a and 106b open by means of a tab (not shown in the drawing) provided on arm 106a which is engaged with the partition wall 103a of slider 103.
A slide mechanism for moving slider 103 in parallel with the bottom surface of the base 102 is provided on both sides of slider 103. The mechanism includes a lever member 108 which is approximately in the shape of an L installed for free rotatable motion at both ends of a shaft 109 which has been provided on one of the edges (the right-hand edge in the drawing) of base 102 and the short arm 108a of this lever member 108 is linked, freely rotatable, to shaft 107 received in vertically extending slots formed in slider 103. In addition, a lever member 111 is mounted, freely rotatable, on both ends of shaft 110 that has been provided on the other opposite side of base 102 and the tip of lever member 108 is mound freely slidable in a slot, at the middle part of lever member 111 by means of a pin 112. Moreover, the tip 111a of lever member 111 engages protuberant part 104a of the ceiling surface of cover 104 when the cover is in its raised position. In addition, there is provided a compression coil spring 113 for biasing the slider 103 to the right as seen in FIGS. 10(a), 10(b).
In a socket 101 made as described above, when the cover 104 is pressed downwardly from the position shown in FIG. 10(a) to that shown in FIG. 10(b), lever members 108 and 111 rotate toward base 102 and, in conformity with the movement of lever member 108, shaft 107 biases slider 103 moving the slider in the X-direction (to the left as seen in FIGS. 10(a), 10(b). As a consequence of this, one arm 106b of contact 106 opens in engagement with the partition wall 103a of slider 103. If, in this state, the BGA package 100 is dropped into the adaptor 103 of slider 103, each solder ball 100a of the BGA package 100 enters between the arms 106a and 106b of a respective contact 106.
When the force upon the cover 104 is released, moreover, the lever members 108 and 111 also rise and the slider 103 returns in the X+ direction by the force of the compression coil spring 113, with a consequence that the arms 106a and 106b of each contact close and that, therefore, each solder ball 100a of the BGA package 100 is held by arms 106a and 106b of each contact 106. As a result of this, each solder ball 100a of the BGA package 100 and each contact 106 can be electrically connected.
In the case of such a socket according to the prior art, however, there has been a problem of inadequate durability of contacts 106 due to a large amount of stress generated in arms 106b because of the fact that, in connection with the mounting of the BGA package 100, the tip part is caused to open by bending arms 106b of the contacts 106. Due to the fact that the center of the opening in which each solder ball 100a is to be dropped shifts by the amount of the opening of one of the arms 106b, there also has been a problem in that, when the amount of the opening of arms 106b has been adjusted, the location, of the drop-in will have to be adjusted so that the solder ball 100a may drop into the proper position. In the case of conventional technology, moreover, in connection with the mounting of a BGA package 100 on a socket 101, there is a situation where the position of the BGA package shifts as the solder ball 100a contacts the tip of a contact 106, with a resultant shifting of the position of the BGA package, thereby causing a contact failure or a mounting failure of the BGA package 100. In some extreme cases, the tip of a contact 106 is sometimes damaged by solder ball 100a of BGA package 100. According to the prior art, moreover, there is a problem in that the solder ball 100a of BGA package 100 and the arms of contact 106 sometimes stick to each other after the completion of the burn-in test, thereby making it difficult to remove the BGA package 100.
An object of the present invention is the provision of a socket which avoids the limitations of the prior art described above. Another object is the provision of a socket with improved durability of the contact members that hold the terminals of an electronic part. Yet another object of the invention is the provision of a socket that is capable of preventing any damage to the biased contact parts of the contact members in connection with the mounting of the electronic part as well as improving the mountability of the electronic part. Still another object of the invention is the provision of a socket which is capable of preventing a failure in the removal of the electronic part subsequent to the test.
In accordance with the invention a main socket body is capable of removable loading an electronic part whose terminals are arranged in the main body part according to a selected pattern. A plurality of contact members are arranged on the main socket body in conformity with the arrangement pattern of the terminals of said electronic part. The contact members each have a pair of arm-like contact parts which are capable of elastically opening or closing in the state of having held a respective terminal of the electronic part. A contact switching member which has an engagement part that engages with the pairs of arm-like contact parts of the contact members opens or closes the arm-like contact parts by the movement of the engagement part. Each arm of the pairs of arm-like contact parts have respectively been made to open or close, with a result that there is no possibility of generating a large amount of stress at one of the arm-like contact parts upon attachment or detachment as in the case of the prior art. Accordingly, it becomes possible to generate uniform stresses by uniformly opening each arm-like contact part. As a consequence of this, it becomes possible by this invention to reduce the maximum bending amount of the arm-like contact parts of the contact members. Accordingly, the durability of the contact members is drastically increased. According to a feature of the invention, the center of opening where the terminal of the electronic part is to be deposited always remains at a constant position as each arm-like contact part opens evenly. Even in the case where the amount of the opening of the arm-like contact parts have been adjusted, therefore, it becomes unnecessary to adjust the drop-in position of the terminals, thereby making it possible to improve the efficiency of the inspection stage.
Accordingly to the invention, further, it becomes possible to increase the compressive force on the terminals of the electronic part compared with the prior art since the compressive force is exerted in opposite directions on the electronic part from each arm-like contact part. Therefore, it thus becomes possible to improve the contact reliability for the electronic part. The force generated is of such a size as is equal in opposite directions against the terminals of the electronic part from each arm-like contact part in connection with the removal of the electronic part from the socket. Compared with conventional technology, therefore, it becomes possible to increase the separation force from the terminals of the electronic part, with a resultant possibility of preventing the possible adherence of the terminals of the electronic part to the arm-like contact parts after completion of the test.
According to a feature of certain embodiments of the invention, the engagement part that engages at least one of each pair of arm-like contact parts of the contact members opens or closes said arm-like contact parts by movement of the engagement part in cooperation with an electronic part seating member provided on the main socket body which moves in conformity with the opening or closing of the arm-like contact parts provided. Thus, it becomes possible in connection with the mounting of an electronic part on the socket to cause relative separation of the electronic part from the arm-like contact parts, thereby avoiding contact between the terminals of the electronic part and the contact parts. According to the invention, therefore, there is no shifting of the position in connection with the mounting of the electronic part, with a result that the mountability of the electronic part can be improved and, at the same time, any possible damage to the biased contact part of the arm-like contact parts can be prevented. According to the invention, moreover, it becomes possible to forcefully pull the connective terminals of the electronic part away from the arm-like contact parts, as by moving the electronic part seating member when the electronic part is detached from the socket. Even in the case where a terminal of the electronic part is fixed to an arm-like contact part, therefore, it becomes possible to accurately take the electronic part out of the arm-like contact parts. In the invention, the realization can be easily achieved when the contact part switching member has an engagement part that engages with each of the pair of arm-like contact parts of said contact members, with said arm-like contact parts being made to open or close through the movement of this engagement part.
According to a feature of one embodiment of the invention, the engagement part which engages with each of the pair of arm-like contact parts of the contact members thereon has a slide member which is capable of sliding in a direction which is approximately normal to the opening and closing direction of the arm-like contact parts of said contact members. According to the invention, it is possible to freely select the opening and closing direction of the contact members. Therefore, it becomes possible to expand the freedom of design including a modification of the opening and closing direction of the contact members. According to one embodiment, the engagement part that engages with each of the pair of arm-like contact parts of the contact members provided thereon has a slide member that is capable of sliding in the opening and closing direction of the arm-like contact part of the contact members.
According to a feature of the invention, a plurality of bores are formed at positions which correspond to the plurality of contact members on the slide member and, at the same time, the engagement part which is adjacent to each of these bores engages at least one of the said arm-like parts of each pair and opens or closes said arm-like contact parts by the up and down movement of the engagement part.
These and other objects of the invention will be apparent from the following description taken with reference to the accompanying drawings.